﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _2023_09_13
{
    internal class _9BuyCard
    {
        static void Main9(string[] args)
        {
            string[] input = Console.ReadLine().Split();
            int k = int.Parse(input[0]);
            int n = int.Parse(input[1]);
            int w = int.Parse(input[2]);

            long totalCost = CaculateCost(k, w);
            long borrow = totalCost - n > 0 ? totalCost - n : 0;
            Console.WriteLine(borrow);
        }

        private static long CaculateCost(int k, int w)
        {
            if (w == 1)
                return k;
            return w * k + CaculateCost(k, w - 1);
        }
    }
}
